The present invention relates to a device and a method for casting strips of metal, in particular steel, in twin-roll continuous casting machines with counter-rotating casting rolls. Liquid metal is fed into a space, bounded by two side walls, between the rotating casting rolls, and liquid metal is prevented from flowing out from gaps that form between the side walls and the casting rolls. The present invention also relates to a device for carrying out the method.
U.S. Pat. Nos. 4,974,661 and 5,197,534 describe methods and devices for the electrodynamic sealing of the side regions of twin-roll casting machines. In the procedure described in these U.S. Patents, magnetic fields are used for the electrodynamic sealing, these fields act over the width of the filling space of the liquid metal and keep the metal away from the side wall over this width. The disadvantages of the conventional methods are that the necessary coil systems are very costly and the currents needed are quite substantial. The installed electric power per seal is 300-500 kW. Further details and characteristic curves of the conventional systems is described in the article: Development of an Electromagnetic Edge Dam (EMD) for Twin Roll Casting, I. G. Sancedo and K. E. Blazek, Metec Conference, Dusseldorf, June 1994, Inland Steel Research and Development.
An object of the present invention is to provide a method and a device featuring substantially lower energy consumption, accompanied by improved adjustability (avoidance of local overheating). Another object is to avoid eddies in the liquid metal that are caused by the sealing. In addition, it is desirable for the sealing device to be markedly smaller and thus more cost-effective than the conventional devices.
The objective is achieved in a device for casting strips of metal with a sealing device that, the sealing device adapts the electrodynamic forces continuously to the metallostatic pressure or approximately to the metallostatic pressure of the liquid metal. In this way, eddying in the liquid metal is avoided. In addition, local overheating is prevented.
In one advantageous embodiment of the present invention, the sealing device is curved in such a way that its distance from the casting rolls increases with increasing height, in particular its distance increases in such a way that, due to the increase in the air gap, magnetic field forces are produced that become weaker and correspond to the metallostatic pressure of the liquid metal which decreases upward.
In a further advantageous embodiment of the present invention, the sealing device has a current-carrying inductor, designed, for example in one piece. The one-piece design has proven especially successful in conjunction with a Y-shaped inductor with two curved branches and a base. In the region where the branches and base are interconnected, the inductor advantageously has a bend configured so that the distance between the casting rolls and the inductor increases with increasing distance from the bend upward and downward. In this way, the forces, caused by the magnetic field are adapted in a suitable manner to the metallostatic pressure of the liquid metal. The forces caused by the magnetic field can be adjusted precisely to the metallostatic pressure if the inductor, in an alternative form to the bent design, is curved in a longitudinal direction, the region in which branches and base meet one another being closest to the casting rolls, and the distance from the casting rolls increases with increasing distance from the part at which branches and base meet.
In a further advantageous embodiment of the present invention, the sealing device has a xe2x80x9cmagnetic shoexe2x80x9d made of magnetizable material. The magnetic shoe is arranged so that the electrodynamic forces are adapted continuously to the metallostatic pressure or approximately to the metallostatic pressure of the liquid metal. The magnetic shoe is particularly suitable for adapting the forces caused by the magnetic field to the metallostatic pressure. It represents an alternative to the bent inductor, but may also be used in conjunction with bent inductor. The magnetic shoe is advantageously V-shaped or Y-shaped, the amount of magnetizable material advantageously decreasing in the direction of the ends of the magnetic shoe. The magnetic shoe is advantageously arranged directly on the inductor, so that it is cooled by the coolant that cools the inductor.
In another advantageous embodiment of the present invention, magnetizable material is arranged at the edges of the inductor, so that the current flowing through the inductor is utilized particularly well in relation to the desired magnetic field, and a lower current is necessary through the inductor.
In a further advantageous embodiment of the present invention, the interspace between the sealing device and the liquid metal is traversed by inert gas, example nitrogen, whereby the sealing device is insulated thermally from the liquid metal.